Method for making differentially coated galvanized steel sheet



SON ERENTIALLY EEL SHEET 28, 1960 3,083,120 COATED March 26, 1963 PATER METHOD FOR MAKING DIFF GALVANIZED ST Filed June hs-L 1 N R mm W 4 N E m 7 m f m .4 I 6 M- 2 m M m o 5 Z V United States Patent 3,083,120 METHGD FUR MAKTNG DEFFERENTIALLY CGATED GALVANTZED STEEL SHEET David Emerson, Draveshurg, Pa, assignor to United States Steel Qorporntion, a corporation of New Eersey Filed June 23, 1950, Ser. No. 39,298 1 Claim. (61. 117-68) This invention relates to the galvanizing of steel sheets and, in particular, to a method and apparatus for making galvanized sheets having a heavier coating on one surface than on the other.

A demand has recently arisen on the part of consumers of galvanized steel sheets for a product having a heavier coating on one side than on the other, and difiiculty has been experienced in making such product. I have discovered a simple method and apparatus which are satisfactory for the purpose and may be readily incorporated in a conventional strip-galvanizing line. Thus, the great productivity of such lines may be taken advantage of in respect to differentially coated as well as standard product (coated equally on both sides).

My invention is based on the discovery that ditferential coating of steel strip introduced into and drawn upwardly out of a bath of molten zinc, will result if the strip emerging from the bath is drawn between exit rolls at about the level of the surface thereof, but one being positioned above the other and one being smooth-surfaced and the other circumferentially grooved. The former should be the upper roll.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the present preferred embodiment. In the drawmgs:

FIGURE 1 is a plan view of a strip-galvanizing apparatus incorporating the invention;

FIGURE 2 is an elevation, partly broken away and partly in section; and

FIGURE 3 is a partial section to enlarged scale taken along the plane of line IIIIII of FIGURE 1.

Referring now in detail to the drawings, a conventional strip-galvanizing apparatus 10 comprises a zinc pot 11 heated by any suitable means (not shown) and containing a bath 12 of molten zinc. Steel strip 13 enters the bath on a downward incline from a snout 14 and passes around a sink roll 15 and then upwardly between exit rolls 16 and 17 journaled in a frame or rig 18 carried on the walls of the pot 11. Except for the novel features more particularly described below, the foregoing apparatus is generally known (Making Shaping and Treating of Steel, published by United States Steel Corporation, 7th Ed., pp. 669-672).

I have found that the desired difference between the weights and thicknesses of the coatings applied to the opposite sides of the strip may be reliably produced by positioning exit roll 16 at a slightly higher level than roll 17 and giving it a smooth surface while providing a helical groove on the surface of roll 17. The groove may be quite small, e.g., ,4 high and 2 wide, and may conveniently form a single continuous helix with a pitch of A. With the described arrangement of the exit rolls, a coating is produced on the side of the strip in contact with smooth roll 16 which amounts to about 0.15 oz./ sq. ft. while the coating on the surface in contact with ribbed roll 17 amounts to about 0.4 oz./ sq. ft., the thicknesses of the coatings being proportional to their weights.

FIGURE 3 shows in greater detail the mounting of rolls .16 and 17 in rig 18. As there shown, the necks of roll 16 rest on a flat horizontal bearing 19 and are disposed against flat inclined bearings 20 keyed to studs 21 threaded into the side plates of rig 18. The necks of roll 17 rest on fiat horizontal bearings 22 and are urged toward roll 16 by flat inclined bearings 23-. Bearings 23 are mounted on the ends of piston rods 24 reciprocating in air cylinders 25 mounted on rig 18 by brackets 26. It will be observed that bearings 19 for roll 16 are slightly higher /4 to /4) than bearings 22 for roll 17. This difference in elevation, together with the fact that roll 16 is smooth and roll 17 is grooved, produces a relatively light coating on the side of the strip engaged by roll 16 and a relatively heavy coating on the other side.

My invention has the obvious advantage of extreme simplicity. It may, furthermore, be incorporated directly in existing high-speed galvanizing lines without reducing their efiiciency or increasing the cost of operation.

The invention may be used for making aluminumcoated strip as well as galvanized strip.

Although I have disclosed herein the preferred embodirnent of my invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

A method of making sheet metal differentially coated with another metal comprising introducing the base metal into a bath of molten coating metal and drawing it upwardly therefrom between parallel cooperating exit rolls at about the surface of the bath, each of said rolls being partially submerged in the bath of molten coating metal; one of the rolls being at a higher elevation than the other, said one roll being smooth-surfaced and the other roll having a circumferential groove.

References Cited in the file of this patent UNITED STATES PATENTS 616,491 Rees Dec. 27, 1898 1,980,961 Sommer Nov. 13, 1934 2,227,976 McLin Ian. 7, 1941 2,759,850 Knopf Aug. 21, 1956 2,950,215 Slater et al Aug. 30, 1960 OTHER REFERENCES Bablik: Galvanizing (Hot Dip), 1950, page 434 relied on, E. & F. N. Spon, Ltd., 22 Henrietta Street, London WC. 2, England. 

